An insole is described in European Patent Specification 0 140 984, formed fro a mixture of silicone rubber and organic filler. This material mixture extends throughout the entire insole, the insole thus being a homogeneous body.
Another insole is disclosed in DE 198 57 568 A1, that insole consisting of a carbon material for stiffening an elastic forefoot, which due to is thickness was also intended to facilitate rolling motion of the foot. That insole had a cork heel pad glued to the ball portion of the insole. That patent specification also made reference to other forms of connection between the ball portion and the heel portion, e.g. an interlocking of the two parts.